HIGHLEVEL REVIEW Chapter 9 Objects and Classes Dr

HIGHLEVEL REVIEW Chapter 9 Objects and Classes Dr. Clincy - Lecture - Ch 9 - Highlevel Review 1

Structured Programming Versus OO Programming Structured Programming Languages Object-Oriented Programming Languages Fortran Java Pascal Python Ada Ruby C C++ BASIC Visual. Basic Top-Down, Subroutines, Functions, Go. To Classes, Objects, Methods Dr. Clincy - Lecture - Ch 9 - Highlevel Review Why OOP ? What is the point ? 2

OO Programming Concepts Object-oriented programming (OOP) involves programming using objects. An object represents an entity in the real world that can be distinctly identified. For example, a student, a desk, a circle, a button, and even a loan can all be viewed as objects. An object has a unique identity, state, and behaviors. The state of an object consists of a set of data fields (also known as properties) with their current values. The behavior of an object is defined by a set of methods. Dr. Clincy - Lecture - Ch 9 - Highlevel Review 3

Objects An object has both a state and behavior. The state defines the object, and the behavior defines what the object does. Dr. Clincy - Lecture - Ch 9 - Highlevel Review 4

Classes are constructs that define objects of the same type. A Java class uses variables to define data fields and methods to define behaviors. Additionally, a class provides a special type of methods, known as constructors, which are invoked to construct objects from the class. Dr. Clincy - Lecture - Ch 9 - Highlevel Review 5

Classes Dr. Clincy - Lecture - Ch 9 - Highlevel Review 6

UML Class Diagram Dr. Clincy - Lecture - Ch 9 - Highlevel Review 7

Constructors A constructor with no parameters is referred to as a no-arg constructor. Constructors must have the same name as the class itself. Constructors do not have a return type—not even void. Constructors are invoked using the new operator when an object is created. Constructors play the role of initializing objects. Dr. Clincy - Lecture - Ch 9 - Highlevel Review 8

Default Constructor A class may be defined without constructors. In this case, a no-arg constructor with an empty body is implicitly defined in the class. This constructor, called a default constructor, is provided automatically only if no constructors are explicitly defined in the class. Dr. Clincy - Lecture - Ch 9 - Highlevel Review 9

Declaring Object Reference Variables To reference an object, assign the object to a reference variable. To declare a reference variable, use the syntax: Class. Name object. Ref. Var; Example: Circle my. Circle; Declaring/Creating Objects in a Single Step Class. Name object. Ref. Var = new Class. Name(); Create an object Assign object reference Example: Circle my. Circle = new Circle(); Dr. Clincy - Lecture - Ch 9 - Highlevel Review 10

Accessing Object’s Members q Referencing the object’s data: object. Ref. Var. data e. g. , my. Circle. radius q Invoking the object’s method: object. Ref. Var. method. Name(arguments) e. g. , my. Circle. get. Area() Dr. Clincy - Lecture - Ch 9 - Highlevel Review 11

Differences between Variables of Primitive Data Types and Object Types Dr. Clincy - Lecture - Ch 9 - Highlevel Review 12

Instance Variables, and Methods Instance variables belong to a specific instance. Instance methods are invoked by an instance of the class. Dr. Clincy - Lecture - Ch 9 - Highlevel Review 13

Static Variables, Constants, and Methods Static variables are shared by all the instances of the class. Static methods are not tied to a specific object. Static constants are final variables shared by all the instances of the class. To declare static variables, constants, and methods, use the static modifier. Dr. Clincy - Lecture - Ch 9 - Highlevel Review 14

Static Variables, Constants, and Methods, cont. Dr. Clincy - Lecture - Ch 9 - Highlevel Review 15

Visibility Modifiers and Accessor/Mutator Methods By default, the class, variable, or method can be accessed by any class in the same package. q public The class, data, or method is visible to any class in any package. q private The data or methods can be accessed only by the declaring class. The get and set methods are used to read and modify private properties. Dr. Clincy - Lecture - Ch 9 - Highlevel Review 16

The private modifier restricts access to within a class the public modifier enables unrestricted access. the default modifier restricts access to within a package Dr. Clincy - Lecture - Ch 9 - Highlevel Review 17

Why Data Fields Should Be private? To protect data. To make code easy to maintain. Example of Data Field Encapsulation Dr. Clincy - Lecture - Ch 9 - Highlevel Review 18

Immutable Objects and Classes If the contents of an object cannot be changed once the object is created, the object is called an immutable object and its class is called an immutable class. If you delete the set method in the Circle class in Listing 8. 10, the class would be immutable because radius is private and cannot be changed without a set method. A class with all private data fields and without mutators is not necessarily immutable. For example, the following class Student has all private data fields and no mutators, but it is mutable. For a class to be immutable, it must mark all data fields private and provide no mutator methods and no accessor methods that would return a reference to a mutable data field object. Dr. Clincy - Lecture - Ch 9 - Highlevel Review 19

Go Over Lab 1 Dr. Clincy - Lecture - Ch 9 - Highlevel Review 20